High-resolution confocal fluorescence thermal imaging of tightly pumped microchip Nd:YAG laser ceramics

A modified two-path confocal microscope was used to obtain fluorescence images of a Nd:YAG microchip element in the presence of a tightly focused 808 nm pump beam. Based on the temperature-induced homogeneous line broadening, high-resolution (< 1 mu m, < 1A degrees C) thermal images of the pump volume and surroundings were obtained from the spatial variation of Nd3+ linewidth. Based on this direct, pure optical and non-contact method, thermal gradients as low as 0.02A degrees C/mu m were detected at focal volume, this being in agreement with theoretical predictions. The thermal imaging technique here presented opens the possibility of accurate compensation of thermal effects for the development of stable and efficient microchip lasers.